Question

A $0.607$ g of a silver salt of a tribasic acid on combustion gave $0.37$ g of $Ag$. Calculate the molecular weight of an acid.

• A. $230$ g/mole
• B. $156.8$ g/mole
• C. $210.6$ g/mole
• D. $188.4$ g/mole

Answer 1

The correct option is C $210.6$ g/mole

Molar Mass of Ag = 108 g

${Ag}_{3}X\to 3Ag$

0.324 g of Ag is produced when 0.531 g of ${Ag}_{3}X$ is reduced

1 g of Ag is produced by $\frac{0.531}{0.324}g$ of ${Ag}_{3}X$ = 1.638 g of ${Ag}_{3}X$

3 Moles of Ag is produced when 1 Mole of ${Ag}_{3}X$ is reduced

$3\times 108$ g of Ag is produced by $1.638\times 3\times 108$ = 531 g of ${Ag}_{3}X$

Molar Mass of ${Ag}_{3}X$ = 531 g

Amount of $X$ in 1 Mole of ${Ag}_{3}X$ = 531 - ($3\times 108$) = 207 g of X

Molar Mass of $H_{3}X$ = 3 + 207 =210 $g/mole$